Sorry, your broken...... No I think that if you are a big guy it would be hard to do a normal situp without anything holding your legs. I can do it, but Im a spindly fuck, but it is still much more effective with my feet under something. Just do crunches with your legs in the air, just pretend they are on a bench.....
yeah, i think that is generally very difficult to do a situp without having your feet held down... some t-mag ab training article from a while ago said that if you could do it, then you had a pretty strong set of abs... i guess i tend to agree w/that statement
it's a strange movement. i always hook my feet under something even though i usually do situp type abs with my legs straight. your feet just naturally want to come up. i think this is pretty common.